Since a photo-polymerizable composition can be used without a solvent, it is preferably used in paint, coating, ink, shaped article as a material in which the load to work environment or terrestrial environment is very small. On the other hand, a photo-polymerizing initiator is essential to cure the photo-polymerizable composition. In the photo-polymerizing initiator, there are a radically polymerizing initiator and a cationically polymerizing initiator.
Although a radically polymerizing initiator has a good performance to show high curing rate, it has defects such as a hindrance to curing by oxygen in air, a shrinkage on curing and the like. Therefore, a cationically polymerizing initiator is more preferably employed.
A photo-acid generator is the substance to release an acid by being exposed to beam, which is useful for cationically polymerizing photo-initiator. Thus, it is used in stereolithographic resin composition and photo-polymerizing composition in paintings, coatings or adhesives. An example of the prior art for such a photo-acid generator, is described in the following Patent document No. 1.
In the Patent document No. 1, an aromatic sulfonium salt compound useful as a photo-acid generator is described, and a cationically polymerizing photo-initiator for epoxy resin, employed the photo-acid generator, and the photo-polymerizable composition employed the initiator are described. Further, a stereolithographic resin composition and a stereolithographic process, employed the composition, are described.
Patent document No. 1:Japanese Patent Application Laid-open No. 2000-186071.(claims, etc.)
A photo-acid generator described in the Patent document No. 1 has a sufficient sensitivity compared with that of the prior art, and provides a photo-polymerizable composition which can be rapidly cure, and a molding having a good precision without the prevention of curing under oxygen. However, the one having the better sensitivity is desirable from the practical view point.
Aryl diazonium salts, which has been used as a cationcally photo-polymerizing initiator in the beginning, has limited usages owing to its bubbly properties and low thermostabilities. Therefore, the sulfonium salts described in the following Patent document No. 2 have been used widely, but nowadays, iodonium salts, which don't release benzene, are used as U.V. curable ink for foods-packaging medium, since a small amount of benzene is released from the sulfonium salt type photo-polymerizing initiator as described in the following Non-patent document No. 1
Patent document No. 2: Japanese Patent Application Laid-open No. 2001-288205
Non-patent document No. 1: Material Stage Vol. 2, No. 2.2002.
However, the iodonium salt described above has a disadvantage such as too short preservative period in summer owing to its low thermostability. Its curability(sensitivity) is also not so good.
Therefore, the object of the present invention is to provide a novel compound useful as a suitable photo-polymerizing initiator being able to give a rapidly and good cured article by effective absorption of the radiation from the source of a ray, a photo-acid generator comprising the novel compound and a photo-polymerizable compositions comprising the same.
And another object of the present invention is to provide a stereolithographic resin composition, by which the above mentioned disadvantages of the prior art can be overcome, the prevention of curing under oxygen do not occur and a molding with desirable dimension can be obtained easily, having sufficient sensitivity to an energy beam to be exposed and to provide a stertlithographic process using the resin composition.
Furthermore, another object of the present invention is to provide a photo-polymerizable composition, which can be used for wide usage, such as an ink for foods-packaging medium, and has improved thermostability and curability(sensitivity), a photo-acid generator, which is useful as photo-polymerizing initiator for such composition, novel aromatic sulfonium salt compound for such photo-acid generator, and U.V. curable ink using the compound.